托福阅读真题Official 54 Passage 2（七）

托福阅读真题Official 54 Passage 2（七）

Overkill of the North American Megafauna

Thousands of years ago,in North America’s past,all of its megafauna—large mammals such as mammoths and giant bears—disappeared.One proposed explanation for this event is that when the first Americans migrated over from Asia,they hunted the megafauna to extinction.These people,known as the Clovis society after a site where their distinctive spear points were first found,would have been able to use this food source to expand their population and fill the continent rapidly.Yet many scientists argue against this“Pleistocene,the period between about 2.5 million and 11,700 years ago during which humans first appeared on Earth,overkill”hypothesis.Modern humans have certainly been capable of such drastic effects on animals,but could ancient people with little more than stone spears similarly have caused the extinction of numerous species of animals.Thirty-five genera or groups of species(and many individual species)suffered extinction in North America around 11,000 B.C.,soon after the appearance and expansion of Paleo-Indians,a group of hunters active in America during the late Pleistocene,throughout the Americas(27 genera disappeared completely,and another 8 became locally extinct,surviving only outside North America).

Although the climate changed at the end of the Pleistocene,warming trends had happened before.A period of massive extinction of large mammals like that seen about 11,000 years ago had not occurred during the previous 400,000 years,despite these changes.The only apparently significant difference in the Americas 11,000 years ago was the presence of human hunters of these large mammals.Was this coincidence or cause-and-effect?

We do not know.Ecologist Paul S.Martin has championed the model that associates the extinction of large mammals at the end of the Pleistocene with human predation.With researcher J.E.Mosimann,he has co-authored a work in which a computer model showed that in around 300 years,given the right conditions,a small influx of hunters into eastern Beringia 12,000 years ago could have spread across North America in a wave and wiped out game animals to feed their burgeoning population.

The researchers ran the model several ways,always beginning with a population of 100 humans in Edmonton,in Alberta,Canada,at 11,500 years ago.Assuming different initial North American big-game-animal populations(75–150 million animals)and different population growth rates for the human settlers(0.65%–3.5%),and varying kill rates,Mosimann and Martin derived figures of between 279 and 1,157 years from initial contact to big-game extinction.

Many scholars continue to support this scenario.For example,geologist Larry Agenbroad has mapped the locations of dated Clovis sites alongside the distribution of dated sites where the remains of wooly mammoths have been found in both archaeological and purely paleontological contexts.These distributions show remarkable synchronicity(occurrence at the same time).

There are,however,many problems with this model.Significantly,though a few sites are quite impressive,there really is very little archaeological evidence to support it.Writing in 1982,Martin himself admitted the paucity of evidence;for example,at that point,the remains of only 38 individual mammoths had been found at Clovis sites.In the years since,few additional mammoths have been added to the list;there are still fewer than 20 Clovis sites where the remains of one or more mammoths have been recovered,a minuscule proportion of the millions that necessarily would have had to have been slaughtered within the overkill scenario.

Though Martin claims the lack of evidence actually supports his model—the evidence is sparse because the spread of humans and the extinction of animals occurred so quickly—this argument seems weak.And how could we ever disprove it.As archaeologist Donald Grayson points out,in other cases where extinction resulted from the quick spread of human hunters—for example,the extinction of the moa,the large flightless bird of New Zealand—archaeological evidence in the form of remains is abundant.Grayson has also shown that the evidence is not so clear that all or even most of the large herbivores in late Pleistocene America became extinct after the appearance of Clovis.Of the 35 extinct genera,only 8 can be confidently assigned an extinction date of between 12,000 and 10,000 years ago.Many of the older genera,Grayson argues,may have succumbed before 12,000 B.C.,at least half a century before the Clovis showed up in the American West.

Question 13 of 14

Look at the four squares[■]that indicate where the following sentence could be added to the passage.One possible nonhuman cause—weather cycles—is not consistent with what scientists know about the timing of the extinctions.Where would the sentence best fit?Click on a square[■]to add the sentence to the passage.

正确答案：A

题目详解

题型分类：插入句子题

题干分析：考察句子和句子之间的衔接判断（通过weather cycles和the timing of the extinctions可以预测后面有可能会讲到气候周期和动物灭绝的时间）。待插入句“一种可能的非人类原因—气候周期—与科学家所知的物种灭绝的时间并不一致”。

选项分析：

A选项后面两句分别提到了气候周期以及灭绝时间，符合插入句内容。

B选项后面一句只说了灭绝时间没有说气候周期，不符合插入句内容。

C选项，插入句没有代词，是一个引出话题句，而不是总结句，所以不应该放在第三句的位置。

D选项后一句有“this coincidence”代词和前一句呼应，此处不能插入句子。

Question 14 of 14

Directions:An introductory sentence for a brief summary of the passage is provided below.Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage.Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.This question is worth 2 points.

About 11,000 years ago,all of North America’s megafauna became extinct.

Answer Choices:

A.

That the first humans migrated to North America near the same time as the extinctions of the megafauna has led many to believe that hunting by humans was a significant cause of those extinctions.

B.

Early North Americans known as the Clovis society developed spears in order to hunt enough large animals to feed their population as it expanded across vast areas of the continent.

C.

Support for the hypothesis that hunting by humans caused the extinctions has been provided by computer models,as well as by the discovery of some mammoths’remains near human settlements.

D.

Scientists have proven that the human hunters of large animals who migrated across North America grew in number so quickly that they killed off most of the megafauna within a few hundred years.

E.

There is more evidence that human settlers hunted large flightless birds like the moa into extinction than there is that hunters caused the extinction of large mammals like the mammoth.

F.

Some scholars argue that the evidence linking mammoth remains to human settlements is insufficient to establish that hunting by humans was a significant factor in the megafauna extinctions.

正确答案：ACF

题目详解

题型分类：文章总结题

题干分析：选择概括性的正确选项。

选项分析：

A选项为第一段和第二段重要信息。hunting by humans was a significant cause of those extinctions对应第一段第二句the first Americans migrated over from Asia,they hunted the megafauna to extinction。near the same time as the extinctions of the megafauna对应第二段倒数第二句The only apparently significant difference in the Americas 11,000 years ago was the presence of human hunters of these large mammals。

C选项为第三、四、五段重要信息。provided by computer models对应第三段第一句championed the model that associates the extinction of large mammals at the end of the Pleistocene with human predation。the discovery of some mammoths’remains near human settlements对应第五段第二句。

F选项为第六段重要信息。the evidence linking mammoth remains to human settlements is insufficient对应第六段第二句there really is very little archaeological evidence to support it。

B选项错误，信息与第一段有关，但是developed spears in order to hunt enough large animals无中生有。

D选项错误，Scientists have proven that过于极端，第一段说的是One proposed explanation，后文也提出了其他对这个说法的质疑。

E选项错误，信息出自第七段，但只在第三句提到，是一个细节论据，不是中心观点。